The first hint of shift-work  I have been able to find dates back to ancient times. The first emperor of Rome, Augustus Caesar, was being pestered by complaints about too much traffic in the cities during the day. He studied the problem and decided that the best way to reduce congestion would be to get rid of some of the horse drawn carriages. A law was passed that created the first night shift and all horse drawn carriages shipping goods were forced to travel at night .
We had to wait over 1800 years after Caesar’s law for the next big development, gas lighting. Candles and oil lamps were replaced by the brighter and more efficient gas lights in the early 1880’s. This development tripled the available work hours and rapidly increased the number of people fighting fatigue during the night shifts and it has kept on increasing ever since.
In 1908, about 2.8% of Western Europeans worked shift-work , in 2001 20% of the world’s working population worked shift-work  and in 2005 28% of all employed Canadians were working shift-work .
In May of 2014, there were 17,830,000  employed people in Canada and 119,000,000 people employed full time in the United States . Using the 2005 figure of 28%, there are now 5 million people in Canada and over 33 million people in the United States working shifts and fighting fatigue every day!
 I include in the shift-work group, any variation of non-standard work hours. If you work outside the standard 9 to 5 range, I consider you a shift-worker.
 Scherrer, J. (1981). Man’s work and circadian rhythm through the ages. In A Reinberg, N. Vieux, & P. Andlauer (Eds.), Night and shift work, biological and social aspects (pp. 1-10). New York: Pergamon Press.
 Pati, A. K., Chandrawanshi, A., & Reinberg, A. (2001). Shift work: Consequences and management. Current Science, 81(1), 32-52.
 Williams, C. (2008). Work life balance of shift workers. Perspectives on Labour and Income, August, 9(8), 3-16.
 See: http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/labr66a-eng.htm
 See: http://www.statista.com/statistics/192361/unadjusted-monthly-number-of-full-time-employees-in-the-us/